U.S. patent number 3,882,496 [Application Number 05/453,477] was granted by the patent office on 1975-05-06 for non-destructive weapon system evaluation apparatus and method for using same.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Gregory V. Cirincione, Virgil D. Lewis.
United States Patent |
3,882,496 |
Lewis , et al. |
May 6, 1975 |
Non-destructive weapon system evaluation apparatus and method for
using same
Abstract
A method and apparatus for nondestructively evaluating the
performance of a eapon system. The unique concept embodied in the
present invention provides nondestructive scoring of weapon systems
during simulated battlefield testing and also provides a technique
of nearly total simulation of the gun laying and firing of a real
weapon system. In a preferred embodiment within the context of an
integrated fire control weapon system, the present invention
includes a gun, a laser, and a radar, all of which are mounted on
separate and independently operable pedestals. The radar or
tracking device supplies position and range information to the
control device which computes the required lead angle and predicted
range which, in turn, defines the point in space where
projectile/target intercept will occur. The gun is then positioned
by the control device in such a way that, if then fired, the
projectile will then pass through the predicted point in space a
time of flight thereafter. Utilizing the same information, a laser
control device positions the laser pedestal so that at the end of
time of the flight of the projectile, the laser will be positioned
towards the predicted point. The laser is fired by the control
device at the precise point in time corresponding to the predicted
intercept time of the projectile and target. The resultant hit or
miss information, which may, for example, be obtained by means of a
laser receiver mounted on the target, is indicative of the total
operational evaluation of the weapon system including the weapon's
target acquisition and tracking devices, the prediction, gun
laying, and projectile performance of the system.
Inventors: |
Lewis; Virgil D. (Silver
Spring, MD), Cirincione; Gregory V. (Rockville, MD) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
23800727 |
Appl.
No.: |
05/453,477 |
Filed: |
March 21, 1974 |
Current U.S.
Class: |
342/54;
434/21 |
Current CPC
Class: |
F41G
3/2655 (20130101) |
Current International
Class: |
F41G
3/00 (20060101); F41G 3/26 (20060101); F41g
003/26 (); G01s 009/02 () |
Field of
Search: |
;343/6R,6A,7ED
;35/25 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hubler; Malcolm F.
Attorney, Agent or Firm: Edelberg; Nathan Gibson; Robert P.
Elbaum; Saul
Government Interests
RIGHTS OF THE GOVERNMENT
The invention described herein may be manufactured, used, and
licensed by or for the United States Government for governmental
purposes without the payment to us of any royalty thereon.
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. Apparatus for nondestructively evaluating the performance of a
weapon system, which comprises:
weapon means for launching a projectile intended to intercept a
moving target;
tracking means for obtaining position and range data of said
target;
first control means responsive to said data for computing the lead
angle and predicted range of said target to define a point in space
where said projectile, if then launched, will intercept said
target;
laser means for illuminating said point in space with a laser beam;
and
laser control means responsive to said first control means for
positioning said laser means at said point in space and for
activating said laser means at the end of a predetermined time
interval.
2. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 1, further comprising servo
means responsive to said first control means for positioning said
weapon means such that said projectile, if then fired, will pass
through said point in space at the end of said predetermined time
interval.
3. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 2, wherein said predetermined
time interval corresponds to the time of flight of said projectile
from said weapon means to said point in space.
4. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 1, further comprising means for
recording information as to whether or not said laser beam has
struck said target at said point in space.
5. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 3, further comprising first and
second pedestal means for mounting said weapon means and said laser
means, respectively, said first pedestal means being responsive to
said servo means and said second pedestal means being responsive to
said laser control means whereby said second pedestal means is
activated during said predetermined time interval; and a third
pedestal means for mounting said tracking means.
6. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 5, wherein said first control
means comprises gun director means for accepting information from
an angle tracker and a range tracker which comprise said tracking
means, said gun director means providing lead angle offset
information to said laser control means.
7. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 6, wherein said laser control
means comprises variable time delay buffer and processor means
responsive to said predicted range and time of flight information
from said gun director means for generating incremental velocity
commands to said second pedestal means, which velocity commands
correspond to the position change required to move said second
pedestal means to the proper position during said predetermined
time interval.
8. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 4, wherein said information
recording means includes a laser receiver mounted on said moving
target.
9. The apparatus for nondestructively evaluating the performance of
a weapon system according to claim 4, wherein said information
recording means includes a laser transceiver as comprising said
laser means, and means for gating said transceiver in response to
said predicted range data from said first control means.
10. In a system which includes weapon means for launching a
projectile intended to intercept a moving target, means for
tracking the target, laser means, and means for controlling said
weapon means and said laser means in response to said tracking
means, a method for nondestructively evaluating the performance of
said system which comprises the steps of:
feeding position and range data of said target obtained by said
tracking means to said control means;
computing the predicted lead angle and range by means of said
control means which defines the point in space where said
projectile will intercept said target if then fired;
positioning said weapon means in response to said computed lead
angle and range such that if said weapon means is then fired, said
projectile will pass through said point in space a predetermined
time of flight of said projectile thereafter;
positioning said laser means during said predetermined time such
that at the end of said predetermined time said laser means is
aimed at said point in space;
activating said laser means by said control means at the end of
said predetermined time such that said laser means emits a beam
which illuminates said point in space; and
recording information as to whether said laser beam has or has not
struck said target at said point in space
whereby the operation of said tracking means, said weapon means and
said control means may be concommitantly evaluated.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to weapon performance evaluation systems,
and more particularly to a nondestructive performance evaluation of
a weapon system which utilizes a laser as a primary component
thereof.
2. Description of the Prior Art
It is often very useful to be able to evaluate the performance of a
weapon system, such as an integrated fire control weapon system,
without the expense and hazard involved in the actual firing of
real weapons and the subsequent destruction of a target.
Present techniques utilized for such nondestructive evaluation of
weapon systems are, however, limited to the evaluation only of the
tracking device of the system. For example, one such system
presently in wide use for such nondestructive evaluation tests is
commonly referred to as a line-of-sight (L.O.S.) laser system. When
utilized in an integrated anti-aircraft artillery system, the LOS
laser is fired when the operator presses the gun firing mechanism
of the weapon. The laser emits a beam in a direction along the line
of sight to the target as defined by the tracking device. Since a
laser can be characterized as a virtually instantaneous device, no
lead angle or gravity correction is necessary to aim it accurately;
hence the laser may be mounted directly on the tracking device, or,
alternatively, the gun-aiming commands of the weapon may be
by-passed and the laser mounted directly on the gun itself. It is
readily apparent that in either of the foregoing cases, total
system evaluation is not possible inasmuch as misses cannot be
evaluated since there is no means of determining the degree of
error involved in a miss. Accordingly, the primary purpose of the
LOS laser scoring is of a psychological nature rather than a
physical one. The only parameter which may be physically evaluated
is the performance of the tracking device which can be accomplished
in terms of the number of hits obtained for each encounter.
Accordingly, it is seen that the use of the LOS laser technique
results in a performance evaluation of the tracking system only,
and fails to take into consideration the essential characteristics
of the gun laying and trajectory performance characteristics of the
weapon under test.
It is seen, therefore, that the LOS laser system falls far short of
accomplishing a total operational evaluation of the weapon system,
which includes not only the performance of the weapon's target
acquisition and tracking devices, but also the prediction, gun
laying, and projectile performance of the system. Accordingly, a
great need exists for a technique and apparatus which would allow
total evaluation of integrated fire control systems under tactical
battlefield conditions which approximates the performance and
operation of the real weapon.
SUMMARY OF THE INVENTION
Accordingly, a primary object of the present invention is to
provide a nondestructive technique for the evaluation of the
performance of a weapon system which takes into account not only
the target tracking capability of a system, but also utilizes, on a
projectile-to-projectile basis, the ballistic and trajectory
information supplied by the controlled subsystem of the weapon.
Another object of the present invention that is to provide a
technique for nondestructively evaluating the performance of a
weapon system which approximates the performance and operation of
the real weapon to a very high degree.
An additional object of the present invention is to provide a novel
and unique method and apparatus for use in the nondestructive
evaluation of the performance of a weapon system which allows total
evaluation of integrated fire control weapon systems under tactical
battlefield conditions.
A still additional object of the present invention is to provide a
method and apparatus for nondestructive evaluation of the
performance of a weapon system which may be easily and
inexpensively adapted to existing laser scoring systems presently
in use and which is adaptable to the evaluation of any type of
weapon system that requires prediction or guidance of the weapon to
intercept its intended target.
An additional object of the present invention is to provide a
technique for evaluating the total performance of a weapon system
that provides nearly total simulation of the gun laying and firing
of a real weapon system without the expense and hazard involved in
the firing of real weapons and the subsequent destruction of the
target.
A still further object of the present invention is to provide a
technique for nondestructively evaluating the performance of the
weapon system which accomplishes the same psychological function as
the prior art LOS laser scoring method, and in addition takes into
account the total system performace from target acquisition to
projectile/target intercept.
The foregoing and other objects are attained in accordance with one
aspect of the present invention for the provision of apparatus for
nondestructively evaluating the performance of a weapon system,
which comprises a weapon for launching a projectile intended to
intercept a moving target, a tracker for obtaining position and
range data of the target while in flight, and a gun director which
is responsive to the data from the tracker for computing the lead
angle and predicted range of the target which defines a point in
space where the projectile, if then launched, will intercept the
target. The apparatus further includes a laser and a laser control
device which is responsive to the gun director for positioning the
laser toward said point in space and which activates the laser at
the end of a predetermined time interval corresponding to the time
of flight of the projectile whereby the laser beam will intercept
the above-described point in space and provide an indication of a
hit or a miss condition taking into account not only the tracking
capability of the system but also the ballistic and trajectory
information supplied by the gun director. The laser is mounted on a
pedestal which may be positioned by the laser control device
independently from the tracking portion of the system. To obtain
this evaluation data, a recording camera could be mounted on, or in
parallel to, the laser pedestal. The camera, if bore sighted with
the laser, would provide a qualitative indication of tracking
and/or prediction errors to be available for post-mission analysis.
The laser control device provides incremental position and/or
velocity commands to the laser pedestal over a predesignated period
of time. At the end of this period, the laser will have been
directed to a predicted point in space and fired, consequently
illuminating the projectile/target intercept point. A preferred
embodiment of such a laser controller is presented within the
context of a self-contained fully integrated weapon system capable
of firing on the move.
BRIEF DESCRIPTION OF THE DRAWINGS
Various objects, features and attendant advantages of the present
invention will be more fully appreciated as the same becomes better
understood from the following detailed description of the present
invention when considered in connection with the accompanying
drawings, in which:
FIGS. 1 through 3 are sequential schematic representations helpful
in understanding the principles of operation of the system of the
present invention;
FIG. 4 is a block diagram illustrating a preferred embodiment of an
integrated weapon system incorporating the novel delayed position
laser of the present invention; and
FIG. 5 is a schematic representation on a time scale which
illustrates a comparison between the delayed laser of the present
invention, the prior art line-of-sight laser, and the operation of
a real weapon system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, wherein line reference numerals
designate identical or corresponding parts throughout the several
views, and more particularly to FIGS. 1 through 3 thereof, there is
depicted therein time sequence schematic diagrams embodying the
principles of the present invention in an integrated fire control
weapon system which comprises a gun 60, a laser 70, a radar or
tracking device 50, all of which are mounted on separate pedestals,
and which are interconnected by means of a controller 40.
Controller 40 may comprise, for example, a computer. Alternatively,
the controller could comprise a digital or mechanical-analog device
such as the one explained in more detail hereinafter with reference
to FIG. 4. One purpose of controller 40 is to provide incremental
position and/or velocity commands to the laser 70 over a
predesignated period of time in response to information received
from tracking device 50. The gun 60 may represent any of a number
of conventional weapons, such as an anti-aircraft artillery gun.
Laser 70 is designated to emit a nondestructive laser beam when
activated by controller 40. The beam width of laser 70 is set to
correspond to the dispersion of the particular weapon 60 to be
simulated. Laser 70, when fired, is pulsed at the fire rate of the
simulated weapon and, although the firing sequence is initiated by
the gunner using the regular gun firing mechanism, the actual
firing of laser 70 is accomplished by controller 40. Laser 70 is
mounted on a pedestal which may be positioned by controller 40
independently from the tracking device 50. In most practical
systems, the laser pedestal may be the gun mount itself. The
tracking device 50, which may comprise a conventional radar,
maintains track of the target, in this instance an aircraft, and
supplies position and range data to controller 40.
Referring now more specifically to the time sequence illustrated in
FIG. 1, radar 50 is seen to be locked on to the target aircraft to
provide position and range data to controller 40. The gun director
within controller 40 computes the required lead angle and predicted
range which defines the point in space (PP) where projectile/target
intercept will occur. Referring now to FIG. 2, controller 40 then
supplies gun 60 with the proper commands to position gun 60 in such
a manner that when the gun is fired, the projectile will pass
through the predicted point in space (PP) a time of flight of the
projectile later. During the same time frame as depicted in FIG. 2,
and utilizing the same information, controller 40 positions the
laser pedestal 70 so that at the end of the time of flight of the
projectile, the laser will be pointed at the predicted point (PP).
Referring now to FIG. 3 in the sequence, the projectile burst will
occur at the predicted point when the time of flight has expired.
Rather than actually fire gun 60, however, at the end of this
predetermined time of flight interval, the laser, having previously
been aimed to this same point in space, will be actuated by
controller 40 so that the laser illumination will occur
simultaneously with the simulated projectile burst at the predicted
point. Gun 60, as seen in FIG. 3, will already have been positioned
for the next projectile; accordingly, in real time, laser 70 will
lag gun 60. If no errors occur, laser 70 will track the target
using information supplied a time of flight of the projectile prior
to its firing.
It is therefore apparent, in accordance with the above brief
description, that controller 40 utilizes not only the tracking data
provided by radar 50 but the prediction data on each projectile
based on the lead angle and time of flight which is supplied by the
gun director in accordance with the information supplied by radar
50. In this manner, the system of the present invention in
evaluating system performance takes into account not only the
target tracking capability but the ballistic and trajectory
information so essential to a complete performance evaluation of
the system. In brief summary, controller 40 positions laser 70 such
that when the time of flight for each projectile has expired, laser
70 is pointed at that point in space where the gun director has
predicted projectile/target intercept. At this point in time, the
controller fires the laser obtaining a hit/no hit condition based
on total weapon performance. To obtain this evaluation data, a
recording camera could be mounted on, or in parallel to, the laser
pedestal. The camera would preferably be bore sighted to the laser
thereby providing a qualitative indication of tracking and/or
prediction errors for postmission analysis.
Depending upon the weapon to be simulated, the subsystem required
to control the laser can be relatively simple in its general
operation, and its function could be performed, for example, by
either a digital or mechanical-analog device. In general, the
purpose of the laser controller is to provide incremental position
and/or velocity commands to the laser pedestal over a predesignated
period of time. At the end of this period, the laser will have been
directed to a predicted point in space and actuated, consequently
illuminating the projectile/target intercept point.
Referring now to FIG. 4, there is depicted a block diagram of a
self-contained, fully integrated weapon system capable of firing on
the move which incorporates the laser controller 40 in a preferred
embodiment incorporating the principles of the present invention.
The system includes a tracking device 50, a gun mount 60, and a
laser pedestal 70, all of which are capable of independent motion.
The tracking and laser pedestals may be mounted on the gun mount.
Each of the three pedestals are gyro-stabilized, not only for
vehicle motion, but also for compensation for the relative motion
between the tracker and laser pedestals and the gun mount. The
system as depicted in FIG. 4 is also seen to comprise a laser
controller indicated generally within the dotted outline at 40, a
gun director 80, a laser fire circuit 95, and a range tracker 90. A
number of adders and subtracters, indicated generally at 52, 54,
56, 58, 62, and 64 interrelate the positional coordinates of
tracker 50, gun 60, and laser 70 in a manner to be described in
more detail hereinafter. The tracking and gun laying functions are
based on inertial coordinates relative to the bore sight of the
tracking device 50. The gun mount 60 is slaved to the tracking
device 50 by means of subtracters 52 and 56, adders 62 and 64, and
lines 66 and 68. Lead angle offsets for both elevation and azimuth
are provided to the gun mount 60 by the gun director 80 by means of
lines 55 and 65 to properly aim the gun (i.e., the predicted lead
angles are added to the slave servos of the gun mount).
During each sample period, the gun director 80 receives angle and
range information from the angle tracker 50 and range tracker 90
along lines 35, 45, and 75, respectively. For the sake of
simplicity, we may assume that the sample rate is equal to the
firing rate of the particular gun to be simulated. In on actual
operating system, however, the sample range would be much higher
(on the order of 100 samples per second) in order to improve the
positioning accuracy of the system, but the functions of the
controller 40 to be described hereinafter would be identical. The
gun director 80, after receiving the angle and range information,
feeds the predicted range and time of flight information to the
controller 40 along lines 41 and 42, respectively. Controller 40
receives the lead angle information (A and B) directly according to
the relative position of the laser pedestal 70 and the gun pedestal
60 along lines 71 and 72. Accordingly, the actual distance through
which the laser pedestal 70 must move during the time of flight is
determined, and, together with the position corrections and
predicted range, is processed and stored in a variable time delay
buffer and processor 85. The acceleration of the axes U and W of
the laser pedestal 70 are received by the controller 40 along with
the rate of roll G of the axes. Cross-coupling correction factors
of the acceleration and rate of roll of the axes are obtained from
device 82, and the resultant velocity and acceleration factors, G,
U', and W' are stored in buffer 85. During each sample period, the
stored velocity in buffer 85 (A' and B') is combined with the
stored position corrections (.DELTA.U, .DELTA.W, .DELTA.G) in a
coordinate converter 88 to produce an incremental velocity command,
A and B, along lines 91 and 92 which is equivalent to the position
change required to move the laser pedestal 70 to the proper
position during the next time interval.
In the foregoing manner, the laser pedestal 70 is positioned over
the time of flight interval, taking into account the corrective
positions due to the motions of the gun mount 60 during the
interval, so that at the end of the interval the laser is directed
at the point in space previously predicted by the gun director 80.
Additionally, during each sample period the controller 40
determines if any previous projectile delay time has expired and
checks the stored fire indicator received from 94 along line 96
corresponding to that projectile. If the time has expired, and the
fire indicator was activated, controller 40 emits a fire command
signal along line 93 to the laser firing circuit 95.
A laser receiver, not shown, mounted on the target, provides an
indication of a hit or a miss of the laser beam thus activated. In
systems where laser receivers cannot be mounted on the target, a
laser transmit/receiver device could be utilized wherein the
predicted range information could be utilized to gate the laser
receiver portion so that a hit/no hit indication could be
obtained.
To obtain this evaluation data, a recording camera could be mounted
on, or in parallel to, laser pedestal 70. The same outputs of
controller 40 as described above may be used to control the
parallel camera if it were mounted on a separate pedestal.
Obviously, the range information is not needed for the camera, but
the laser fire command along line 93 may be used to trigger an
indicator within the camera's field of view so that information
pertaining to the activation of the laser would be available for
post-mission analysis.
FIG. 5 is helpful in illustrating a comparison between the prior
art line of sight laser, the delayed position laser of the present
invention, and a real gun system. The vertical labels on the
left-hand side of FIG. 5 represent the two conditions (A and B)
under which a firing sequence might occur for the LOS laser, the
firing sequence for the delayed position laser of the present
invention, and the firing sequence for a real gun system. The
horizontal axis represents time, each block representing an instant
in time during which the indicated event may be initiated or
performed, as the case may be. All devices are assumed to be
mounted independently on their own pedestals. Obviously, in real
time, some of these events may occur nearly simultaneously, but for
the purposes of illustration, such events are represented by
consecutive time frames.
Referring first to the real gun system, the data to be used by the
gun director is gathered or smoothed over some period of time
T.sub.s to T.sub.o. The gun director calculates the predicted angle
at time T.sub.o then commands the gun position at time T.sub.1
whereafter the gun fires the projectile at time T.sub.f. After the
projectile has been fired, there exists a period of time
(projectile time of flight) which is unique to each projectile.
This time of flight is represented by the time period from T.sub.f
to T.sub.i. At the expiration of this time interval at time
T.sub.i, projectile/target intercept occurs at the point in space
previously predicted (assuming no error) by the gun director.
Referring now to the firing sequence for the line of laser,
sequences A and B depict two possible conditions under which the
LOS laser might be fired. Sequence A begins at the same point in
time T.sub.s as that of the real gun system. the data gathering
period from time T.sub.s to T.sub.o may be the same, but the
predicted angle and position of the laser is not. Since the LOS
laser does not require a lead angle (i.e., it is customarily
mounted on or in parallel with, the tracking device), it requires
only the data supplied to the tracking pedestal to maintain a
direction toward the target. Therefore, at time T.sub.o and
T.sub.1, the LOS laser sequence deviates from the gun sequence
completely. Accordingly, when the laser is fired at time T.sub.f,
even though it may illuminate the target, all that is accomplished
is an evaluation of how well the tracking device has followed the
target. With respect to sequence B, if the laser is fired so that
it illuminates the point in space where the protectile would have
intercepted the target (this would occur strictly by coincidence,
since no projectile time of flight is calculated in the LOs laser
scoring technique), it has not used the same data as the gun
utilized to establish its position commands. Accordingly, the use
of the LOS laser technique results in a performance evaluation of
the tracking system only, and does not take into consideration the
gun laying and trajectory characteristics of the weapon under
test.
The delayed position laser firing sequence according to the present
invention performs identically to the real gun system up to and
including the positioning of the gun. The same data is utilized for
the prediction from time T.sub.s to T.sub.o. The same predicted
angle and gun position is output by the gun director at times
T.sub.o and T.sub.1. Only at time T.sub.f does the sequence deviate
from that of the real gun system, and that deviation is relatively
minor. At time T.sub.f, instead of firing the laser, the technique
of the present invention initiates the laser controller 40 (of FIG.
4) which positions the laser during the delay time from T.sub.f to
T.sub.i, the identical interval of time as the projectile time of
flight in the real gun system. Accordingly, at time T.sub.i, the
laser will be directed at the point in space where the
projectile/target intercept will occur. This is the same point in
space described above with reference to the real gun system. At
time T.sub.i, a laser controller will fire the laser and the beam
therefrom will illuminate the intercept point.
Accordingly, it is seen that we have provided a method and
apparatus for nondestructively evaluating the performance of a
weapon system which takes into account not only the target tracking
capability of the system, but also utilizes, on a
projectile-to-projectile basis, the ballistic and trajectory
information supplied by the director subsystem of the weapon. Since
the system of the present invention utilizes the same data used in
the actual firing of the weapon, the present technique approximates
the performance and operation of the real weapon to a degree
heretofore unobtainable. Accordingly, the present invention allows
total evaluation of integrated fire control systems under tactical
battlefield conditions. It will be understood by those skilled in
the art that with the addition of a controller to the laser scoring
systems presently in use, the present invention may be utilized to
evaluate a wide range of weapons from anti-aircraft artillery
systems to self-contained mobile missile systems, that is, any type
of weapon that requires prediction or guidance to intercept its
intended target.
It will be appreciated by one skilled in the art that, with the
exception of gun vibration and perturbation of the flight path of
each individual projectile by the environment, the real gun system
has been totally simulated by the technique and apparatus of the
present invention on a projectile-to-projectile basis. The target
has been allowed the same amount of time as it would have against a
real gun to maneuver or evade the weapon during the projectile time
of flight. In some cases where a relatively long time of flight and
a highly maneuverable target are involved, this time factor could
be of great significance in the tactical evaluation of a weapon
system. Prior art scoring systems take the foregoing into account
only on a general basis during post-mission processing and
analysis. It is also apparent that the perturbation of the flight
path of each projectile could be successfully simulated by
inserting a random error into the positioning servo for each
projectile; accordingly, the effects of the environment and the gun
vibration on the projectile path can be made to approach those of
the real weapon.
We wish it to be understood that we do not desire to be limited to
the exact details of construction shown and described, for obvious
modifications can be made by a person skilled in the art. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described herein.
* * * * *